Hydraulically operated machine tool



April 24, 1951 L. G. L. THOMAS 2,550,391

HYDRAULICALLY OPERATED MACHINE TOOL Flled Nov 3 1945 3 Sheets-Sheet 1 INV ENT OR.

A A ril 24, 1951 L. e. 1.. THOMAS 2 I a g m ANN J \..M\ W m m f w a Q 7 u f m m L k M m u 3% m a w a \N Y n W N\ w B m Q N \x w m h w m g Rw mw m M N a N Mo N I m kw Brew m M Q m m MN h w al 70 W N d e 1 m Patented Apr. 24, 1951 v UNITED STATES ATENT OFFICE Louis G. L. Thomas, Glendale, Ohio, assignor to Liberty Planers, Hamilton, Ohio, a partnership Application November 3, 1943, Serial No. 508,829

3 Claims.

hydraulic table actuating system which is simple and convenient to construct, less expensive and cumbersome than the units heretofore employed, and particularly free from chatter when the machine is being operated under load conditions.

A further objective of the invention has been to provide a hydraulic mechanism in which a plurality of cutting speeds may be obtained in conjunction with a plurality of rapid traverse feeds through which the table may be returned after a cuttin stroke has been completed.

In a machine like a planer, where the length of table movement is substantial, it is desirable to provide a mechanism in which the rate of travel at which the table is returned is substantially greater than the speed during cutting. There is, consequently, a substantial difference in the volume of fluid required during the cutting stroke and during return traverse. On the other hand, the pressure of the fluid during cutting must be many times greater than the pressure required to return the table under no load conditions.

This invention, briefly, is predicated upon the concept of employing a relatively small positive pressure pump to furnish the limited volume of hydraulic fluid at the high pressure which is required during cutting, and to employ a centrifugal pump for furnishing the large volume of fluid at low pressure to provide for rapid table traverse. In this manner the size of the more expensive positive acting type of pump requiredfor high pressure operation is kept at a minimum while the large volumes of fluid at low pressure which are necessary during the return stroke are furnished through an inexpensive centrifugal pump unit.

In preferred embodiments of the invention, though not necessarily, the positive displacement pump operates either directly against the pressure of the centrifugal pump discharge during the cutting stroke or against back pressure furnished through a metering circuit whereby, in either event, a predetermined loading of the table is obtained to prevent any chattering or undulating movements which otherwise might take place, especially if the cut is discontinuous. In

the former instance, hydraulic fluid previously introduced into the hydraulic ram during a return stroke is discharged through the centrifugal pump in a direction of fiow which is opposite the normal centrifugal pump discharge. At the end of the cutting stroke infeed from the positive displacement pump is diverted from the actuating cylinder whereupon the pressure of the fluid discharged from the centrifugal pump immediately causes the table to move in an opposite direction.

Speed of return traverse is controlled conveniently either by throttling the centrifugal pump discharge, or by diverting a portion of the discharge through a bypass in such manner that continuous circulation is provided to prevent overheating of the fluid. In place of having the discharge from the :positive displacement pump and the centrifugal pump act upon opposite ends of a piston in a single hydraulic cylinder two cylinders operate in opposite directions may be employed respectively to receive the high and low pressure pump discharges, Control or pilot valves are provided for shiftable diversion of the fluid flow at the end of the cutting and return strokes and such valves may be operated automatically through adjustable dogs provided at the table.

From these principles upon which the present invention is based and from the following detailed description of the preferred embodiment of the structure shown in the drawings, those skilled in the art readily will comprehend the modifications to which the invention is susceptible.

Inthe drawings:

Figure l is a plan view of a planer bed and table showing the pump and ram arrangement. In this figure and in the other illustrations of the drawings, the rail and its tool carrying saddle and feeding mechanism are omitted; they may be of the usual double housing, convertible, or open side type.

Figure 2 is a side elevation of a planer bed and table therefor equipped in accordance with the present invention.

Figure 3 is an end elevation of the bed and table showing portions of the hydraulic circuit.

Figure 4 is a representative hydraulic circuit in which centrifugal and positive displacement pumps cooperate with one another in accordance with this improvement.

Figure 5 is a diagrammatic view of an alternative type of circuit wherein a pair of hydraulic rams operating in opposite directions are employed to actuate the table through its cutting and reverse strokes.

3 The invention may be understood most conveniently by reference to Figure 4 in which the various glements shown diagrammatically are illustrate; l structurally in the other figures.

High pressure circuit A positive displacement pump is indicated generally at l, in Figure 4. It may be a pump of the constant volume or variable displacement type suitably driven by a motor to develop pressure suificiently high to drive the table and the work mounted thereon past the tool during cutting operations. The pump 1 has its intake line 2 connected with a sump 3 located :'between the side walls of the bed or at the side thereof. In the latter arrangement the positive pressure pump and driving motor are mounted directly over the sump for accessibility.

The pump i discharges through a line i to a pressure relief valve 5 which has a vent line 6 leading from it to the sump 3 for return of the relieved fluid. Thus, if the table for any reason becomes blocked against movement the relief valve actuates to preventdamage to the appara tus. 'Beyond the relief valve the high pressure pump discharge passes through a line i, to a three-way valve indicated generally at8, then on through a line 9 to the hydraulic ram It, the line 9 containing a throttling valve l l for controlling cutting speed. Ram Iii comprises a casing having a piston carried by a cylinder rod, these members being relatively interconnected between the table and the bed to effect movement of the table in one direction on the bed when fluid under high pres- ,sure is introduced into the cylinder at one side of the piston.

One suitable type of valve 8, as shown in the drawings, comprises a chamber !2 having a plunger i3 'slidably arranged within it. The plunger has two annular grooves M and i5 delineating between them a blocking portion it. The stem of the plunger which extends beyond the chamber at one end thereof is arranged to be moved either manually or by means of dogs mounted'on the planer table, whereby the valve may control the cutting cycle. Vent lines i l and i8 enter the valve chamber 8 at the opposite sides of the pump discharge line I and these, in turn, are interconnected with one another through a conduit I9 passing to the sump 3. Figure 4, is shown in'the position which it occupies when the table has just completed a return stroke and just before it is set toeffect movement of the table in a cut direction. In this position discharge from the pump I passes through the line 7, through the annulus iii in the valve plunger, and out through the lines I! and Hi to the sump 3.

To effect a cutting stroke the Valve plunger is lifted causing the portion [6 of the piston to be moved to the opposite side of the-inlet port, thereby isolating the vent line i l; the lower portion of rthe plunger, at the same time, moves over the port connected with the return line I8. Thus, fluid under pressure is directed from the line 1, through the annular recess i i and into the hydraulic ram I through the conduit 9. The throttling valve ll enables the operator to vary the cutting speed at will by controlling the volume of high pressure fluid which is introduced into the ram.

Low pressure circuit In the circuit shown in Figure 4, the pump arranged to deliver substantial volumes of fluid at The valve, in

low pressure for rapid return traverse of the table is indicated generally at 2|. This pump is of the centrifugal type and may be driven suitably by means of an independent motor 22 or the pump 2| may be driven in unison with pump l by motor 23.

Hydraulic fluid is taken from the sump 3 to the centrifugal pump through a conduit 24 and pump .2l discharges to a line 25 which, in turn, is connected, through a line 26 to the hydraulic cylinder at the end thereof opposite the end at which :high pressure fluid is introduced. For bypassing the pump discharge, a line 2? is inter-connected between line 25 andthe sump 3. The bypass line iwhichmay containa throttling valve 28 provides for recirculation of the discharge from the cen- ,trifugal pump 2!, whereby the hydraulic fluid is prevented from becoming overheated even though -,the machine is out of operation for a substantial period of time during which the centrifugal pump may be operating. A two-way pilot operated valve 28a may be included in the line 25 to provide control whereby "the table may be inched gradually to a given position.

In the operation of the circuit which has just been described, it maybe seen that both the centrifugal pump 25 and the positive displacement pump I may operate continuously, the centrifugal pump furnishing fluid to return the table at rapid traverse speeds following each cutting stroke and also furnishing fluid under low pressure to act as a load or steadying tension on the table for preventing chattering during cutting strokes and to provide uniformity in the speed of table movement. Thus, with the cutting stroke '1 the cylinder, returning to the sump 3 through the bypass line 2'! or through the pump 2'! in reverse flow, the actual course depending upon the setting of valve 28.

At the end of the cutting stroke the valve 8 :is moved to the position which it occupies in Figure 4, whereupon the high pressure discharge .from the pump is 'diverted through the line 19 to the sump. At this time fluid from the centrifugal pump Zi enters the cylinder to efiect return traverse of the table, and the discharge of fluid from the opposite .end of the cylinder proceeds through the line 9 through the anular recess M at the valve 18, and through the vent line I8 to meet the .pump'discharge'of pump l,'which is now by-passing at theline 1.9 for return to the sump. By virtue of this arrangement there is no tendency for the discharge from the high pressure pump to block the flow of fluid being expelled from the ram.

The circuit just described is a simple system in which centrifugal and positive displacement pumps cooperate for traverse of the table through its cutting and return strokes.

A variable loading the 'ta'ble during cutting may be obtained through a supplemental metering circuit which is indicated at 2% in Figure *4. This circuit comprises a conduit 3i? interconnecting the line 25 with a metering valve 3i, with a return line 32 extending therefrom to the sump 3. In the event this flow control circuit is used, a check valve 32a, may be installed in line "25 ahead of the inlet to the hydraulic cylinder,

whereby back flow from the cylinder through the pump or bypass line 28 is blocked. The flow control meter 3% serves the purpose of maintaining a back pressure in the hydraulic cylinder during the cutting stroke. It is to be observed. that the valve 3| is set to pass hydraulic fluid at a pressurewhich is greater than that required to effect movement of the table in a return direction.

Thus, when high pressure fluid from the pump l is being introduced through the line 3 into the one end of the hydraulic cylinder to produce movement of the table in a cutting direction fluid expelled from the cylinder at the opposite end is blocked against flowing through the centrifugal pump 2| or relief circuits because of the check valve 32a and therefore proceeds through line 30, valve 3|, and line 32 to return to the sump. However, the flow control unit 3! restricts the flow through this circuit to maintain a predetermined back pressure at the cylinder ill to provide predetermined resistance to table movement. The flow control device 3! of the metering circuit may be of various types, one suitable unit commercially available being the Vickers Flow Control F x-2112B.

At the end of the cutting stroke hydraulic fluid passes directly from the centrifugal pump into the cylinder to efiect rapid return movement of the table.

As shown in Figures 1, 2 and 3 these control units for both the high and the low pressure circuit are mounted. conveniently upon the bed of the machine at points accessible to the operator, the pilot valves being located adjacent the table for dog actuation. Inasmuch as the valve and control units are conventional the structural details are not shown.

It is to be noted that multiple cutting speeds readily may be obtained by the employment of a constant delivery positive pressure pump and multi-speed motor for thehigh pressure circuit of the apparatus with a constant "speed motor operating the centrifugal pump, and a variety of rapid traverse speeds being obtained through throttling of the centrifugal pump discharge. The high pressure pump, which necessarily is of more precise construction and therefore much more expensive to manufacture than the centrifugal pump, need have only the capacity to furnish fluid for the cutting speeds without the excess capacity which otherwise would be required merely for returning the table at low pressure.

The structure shown in Figure comprises a high pressure positive acting pump and a low pressure high volume centrifugal pump for the purposes which previously have been described but these pumps respectively feed hydraulic rams which are oppositely arranged to drive the table through its cutting and. return strokes. This modification provides the advantage of enabling the high pressure system to be located at one end of the table and the low pressure system at the opposite end therebyavoiding friction losses and the pressure drop attending the passage of fluid through pipe lines of substantial length.

The hydraulic rams are mounted in side by side relationship between the table and the bed, the ram 33 causing movement of the table in a cutting direction and the ram 3% in a reverse direction. In the preferred embodiment the cylinder of each ram is carried by the table and moves with it, the ends of the cylinders respectively being buttressed against suitable bosses 35 and 35a extending from the table. The pistons are fixed tothe bed and hydraulic fluid may be introduced in any suitable'manner as for instance through openings in the piston rods. In the high pressure circuit the positive acting high pressure pump indicated generally at 36 is mounted upon a sump 3'! which is located adjacent one end of the machine for instance between the side walls of the bed. This pump discharges through a line 38 to a dog actuated three-way valve 39 which is similar in construction to the valve 3 previously described in connection with Figure 4.

A conduit 48 extends from the valve 39 into connection with the cutting ram 33 and this line also may contain a throttle valve through which inching control of the table may be exercised. Intermediate the pump 36 and the valve 39 a relief circuit dl is connected. with the sump ti and this circuit contains a suitable relief valve 52 while return lines 43 and M are also taken to the sump through the line 4! to accommodate back flow of hydraulic fluid from the cutting ram 33 during movement of the table in a return direction. Thus, upon actuationof the plunger in valve 39, the pump discharge line 38 communicates with the line M) and high pressure fluid enters the ram 33 to actuate the table in a cutting direction. At this time the outlet ports is and 63 are isolated. Reverse actuation of the valve as breaks communication of the lines 38 and w and hydraulic fluid may then drain from the line it through the lines 44 and 4| to the sump iii.

In the low pressure circuit the centrifugal pump is indicated at 45. It is connected through a line at with a sump d! and discharges to a line 48 which extends to the low pressure or return ram ed. A check valve 49 is located in the conduit 48 arranged to prevent return flow through the pump and a throttle valve 50 also is provided for inching control of the table under the actuation of the low pressure pump. Between the check valve 49 and the inching control valve 50 a return line 5| is taken to the conduit 46 extending from the sump and this circuit contains a metering valve 52 which has the same purpose as the valve 3| described in connection with Figure 4 and also contains a throttle valve 53 having a pilot thereon positioned to be actuated by dog means located on the planer table. Thus the check valve 49 causes hydraulic fluid to pass from the centrifugal pump 45 to the ram 34 to effect movement of the table in. a return direction while hydraulic fluid expelled from the ram 34 during table movement in an opposite direction is diverted through the flow control device 52 whereby a steadying force is exerted upon the table during cutting. The metering circuit also provides for recirculation of fluid to prevent overheating during periods in which the table is not being actuated.

Having described my invention, I claim:

1. A hydraulic actuating system, comprising a hydraulic cylinder and piston slidable therein, a centrifugal pump, a positive displacement pump, a reservoir, means including a valve for directing fluid from said positive displacement pump into the cylinder at one side of said piston to effect an actuating movement in one direction and then to divert the flow of fluid from said pump to said reservoir, means for directing discharge from said centrifugal pump into the cylinder at the opposite end of said cylinder continuously, a check valve in said continuous centrifugal pump discharge line before the inlet to said cylinder to c ssogac i 7 check "the return flow to said centrifugal pump, and ame'tering circuit connected with said cylinder "beyond said inlet point for metering the expulsion of oil therefrom under movement of said cylinder efiected by introduction of fluid from said high pressur pump.

2. A hydraulic actuating system for efiectin translation of the reciprocating element of a machine tool in which work is performed on a workpiece in one direction of travel of said element onlyjsaid system comprising: a hydraulic cylinder and iston slidable therein, a centrifugal pump, a positive displacement pump, a reservoir, means including a valve for directing fluid from said positive displacement pump into the cylinder at one'side of said piston to efiect an actuating movement thereofin one direction and then to divert the flow of fluid from said pump to said reservoir, an actuating member mounted upon the reciprocating element and cooperating with the valve to shift said valve to and from the said cylinder-flow directing positions respectively at the'limits of travel of said reciprocating element, the face of the said piston which develops workproducing pressure having an effective area not greater than the opposite face thereof, and means :pump, a positive displacement' pump, a reservoir,

means including a valve for directing 'fluid from 8 said positive displacement pump into the cylinder at one side of said piston to 'efiect an actuating movement thereof in one direction and then to divert the flow of fluid from said pump to-said reservoir, an actuating member mounted upon the reciprocating element and cooperating with the valve toshift said valve to and from the said cylinder-flow directing positions respectively at the limits of travel of said reciprocating element, a rod mounted on that side of said piston which develops Work-producing pressure, said rod extending through an end of the cylinder and having its outer end connecting to said reciprocating element for translation therewith whereby said rod is under tension during the work stroke, and means for directing discharge from said centrifugal pump into the cylinder at the opposite end of said piston continuously.

LOUIS G. L. THOMAS.

-REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,619,474 Hubbard Mar. 1, 1927 1,663,513 Howse Mar. 20, 1928 1,725,489 Stratton Aug. 20, 1929 1,822,690 De Leeuw Sept. 8,1931 1,866,348 Ferris et a1 July 5, 1932 1,937,052 Bausman 'Nov. 28, 1933 1,985,443 Clute Dec. 25, 1934 2,016,654 Shippy et a1. Oct. 8, 1935 2,118,020 Curtis May 17, 1938 2,148,348 Groene et a] Feb. 21, 1939 2,262,126 Whittles Nov. 11, '1941 

